Process for the wet-spinning of acrylonitrile polymers



Jan. 15, 1963 L. NOTARBATOLO ETAL 3,073,670

PROCESS FOR THE WET-SPINNING OF ACRYLONITRILE POLYMERS Filed July 10, 1961 INVENTORS LU lGl NOTARBARTOLO ALBERTO PASIN ATTORNEY 5 United States Patent 3,073,670 PROCESS FOR THE WET-SPINNING 0F ACRYLO- NITRILE POLYMERS Luigi Notarbatolo, Milan, and Alberto Pasin, Cesano Maderno, Italy, ass'ignors to Siuia Vis'cosa Societa Nazionale Industria Applicazioni Viscosa S.p.A., Milan,

Italy, a company of Italy Filed July 10, 1961, Ser. No. 123,955 Claims priority, application Italy July 18, 1960 Claims. (Cl. 18-54) It is an object of the present invention to provide a wet-spinning process for acrylouitrile polymers as well as the coagulating and stretching baths for carrying it out. The expression acrylonitrile polymers includes in the present specification, polyacrylonitrile as well as polymers, co-polymers, graft polymers and mixtures of polymers of acrylonitrile.

It is known to spin acrylonitrile polymers by the wetspinning method, viz., by dissolving them in volatile organic solvents, in particular organic solvents miscible with water, and extruding the solutions into a suitable coagulating bath, the resulting filaments being thereafter stretched in a suitable stretching bath. The organic solventmost frequently .used is dimethylformamide. Known coagulating and stretching bath compositions include calcium chloride, zinc chloride, zinc bromide, zinc iodide, andpotassium acetate solutions.

It is an object of the present invention to provide a wet-spinning process that permits to obtain yarns having good mechanical characteristics, glossyappearance, free from cavities in the filaments, and possessed of good dyeing properties.

It is another object of the present invention to facilitate the recovery of the organic solvent employed to prepare the solutions of acrylonitrile polymers.

The process according to the invention comprises extruding a solution of an acrylonitrile polymer in an organic solvent miscible with water, into a coagulating bath and thereafter stretching the resulting. filaments in a stretching bath, both baths consisting essentially of aqueous solutions containing from 30 to 75% by weight of potassium formate. The coagulating bath as well as the stretching bath may also containand as a rule containeven considerable amounts of the organic solvent used to prepare the solution of acrylonitrile polymer. Preferably said amounts are not less than 0.5% and not more than 30% by weight of the bath. The coagulating and the stretching bath often has the same composition.

. Coagulation preferably takes place at low temperatures C.50 C.) while higher temperatures, for instance between 115 C. and M0" C., are Preferred for stretch- By the process according to the invention it is possible to prepare continuous filament yarns from spinnerets with only a few orifices or to prepare tow or staple from spinnerets with a large number, up to 15,000 and more, of orifices. If high-tenacity yarns are desired, high concentrations of potassium formate in the baths, and high stretching temperatures are used; under such conditions degrees of stretching as high as 1500% can be attained. In general, all other conditions being equal, the higher the concentration of thepotassium formate coagulating bath, the higher is the degree of stretching that can be attained.

The length of immersion of the yarnin the coagulating bath should be sutficient to produce a complete coagulation of the filaments. Said length depends not only on the number of orifices of the spinneret, but also on their diameter and, therefore, on the count of the desired filaments, and preferably varies from to 200 cm.

The speed with which the filaments are drawn from the ice coagulating bath varies generally from 4 to 10 metres per minute. On leaving the coagulating bath the'fila: ments are collected on a storage and advancing device for instance on a reel consisting of meshing cages or, on a plurality of rolls, according to,whether continuous filajment thread or 'staple'fibre is to be produced; then they are passed into thestretching bath from which they are drawn by another storage and 'advancingdevicefor instance of the same kind, at a linear speed multiplied by the stretching ratio, for instance between 30 and 'metres per minute. The length of immersion of the filaments in the stretching bath varies preferably between 30' and 200 cm.

After stretching, the filaments are washed with'water until the potassium formate and the solventhave'been completely'eliminated, then'they are allowed to retract, dried and collected on cones or cut to staple. All these operations are carried out by conventional techniques so that it is not necessary to describe them in detail.

They are illustrated on the attached diagrammatic drawing. In the drawing 10 is a reservoir of acrylonitrile polymer solution, 11 is a spinneret, and 12 is a coagulating bath. The filaments 13 thus'formed are-drawn from bath 12 by a multiple roll device 14 and fed into a stretching bath 15 from which they are drawn by a higher speed multiple roll device 16. They pass thereafter through a plurality'of washchambers'17, are allowed to retract in chamber 18, are dried in chamber 19, are passed over finishing roll -20, and are finally wound on cones 21, or could optionally be cut into staple.

The following examples illustrate the embodiment of the invention. The parts and percentages are all by weight.

Example 1 A viscous solution is prepared which is composed of 17 parts of polyacrylonitrile having a molecular weight of 60,000 and 83 parts of dimethylformamide.. The solution is extruded through a spinneret having 60 orifices of 80 micron diameter in a bath kept at 25.? C. and C011, sisting of a clear solution containing 51% of potassium formate, 15% of dimethylformamide and 34% of water, having a density of 1.33 at 20 C. The yarn travels in this bath over a distance of 40 cm. and is drawn there from at the linear speed of 7 meters per minute. Then it passes into the stretching bath kept at C.and con? sisting of 60% of potassium formate, 2% of dimethylformamide and 38%, of water. The yarn travels over more than 40 cm. in the stretching bath and is stretched in a ratio of 10:1 so that it is drawn therefrom at a speed of 70 metres per minute. bleaching, drying and finishing, the yarn is collected in small cones and has the following mechanical properties measured on the individual filaments: filament count=3.4l den., tenacity (after conditioning at 20 C. and 60% R.H.)=4.5 grammes/den., elongation at break (after conditioning as above) =11%.

The cross-section of the filament is approximately round. The high water-solubility of patassium formate, thelow viscosity and the low surface tension ofits aq eous solutions as compared with other solutions commonly used, render the coagulation and washing and,

therefore, the removal of the salt from the filaments,

easier and more uniform.

Example 2 A viscous solution like that of Example 1 is extruded through a spinneret having 15,000 orifices of 80 micron diameter into a coagulating bath of the same composition as in Example 1. The filaments are drawn therefrom at a speed of 7 metres per minute. The length of travel in the coagulating bath is 80 cm. The filaments After washing with Water, 7

, 3 are then-passed through a stretching bath having the same composition as in Example 1, at a temperature of 120 C. The filaments remain immersed therein for 50 cm. and are drawn therefrom at a speed of 60 metres a minute. On leaving the stretching bath the filaments are washed, bleached; retracted, dried and crimped continuously, collected as a towor cut as a staple to the required length. The mechanical properties measured on the individual filam'ents are: filament c'ount =3.2 den, tenacity (after conditioning)=3.5 grammes/den, elongation at break (after conditioning)=%. As is known, in wet-spinning processes of this kind it isneces'sary to'recover the volatile organic solvent used to prepare the spinning solution and to prevent its accumulation in the baths. It is known to effect this recovery by extracting said solvent fromthe coagulating and stretchingbaths by means of suitable organic extracting liquids. i

Various liquidswere proposed heretofore such as amyl chloride, allyl chloride, methylene chloride, and dichloroethylene. In a co-pending application of the same applicants 'there are described new extracting means such as methyl, ethyl, iso pr'opyl and ri propyl for-mates, and methyl, ethyl, iso-propyl and n-propyl acetates. The economy of the-extracting process depends on the coefficient of distribution of the organic solvent to be recovered, between the extractingmeans and the bath containing it; The expression coefiicient of distribution 'me'ans herein the ratio between the percentage by weight of the solvent, for instance dimethyl formamide, contained in .the extracting liquid and the percentage by weight of the same remaining in the extracted bath, after the extraction, viz:

Percent of solvent in the extracting medium Percent of solvent in the-extracted bath The higher the coefficient of distribution, the more economical is the recovery of the solvent.

Now it has been surprisingly found that if coagulating and stretching baths based on solutions of potassium formate are used, the coeflicient of distribution, especially if the solvent is dimethylformamide, with respect to the extracting liquids previously known or those proposed in the above mentioned co-pending application of the same applicants, is considerably higher than that found when previously known baths are used. While in the latter case it is generally not more than 3, it rises to' about 7-8 when potassium formate baths are used. Consequently, other conditions being equal, a larger quantity as organic solvent, in particular of dimethylformamide, is extracted from potassium formate baths less solvent remains in theextracted-baths. This constitutes an important result and an advantage of the present; invention.

Said advantage will be illustrated by a dimethylforma-v mide extraction test carried out with a known extracting medium, namely methylene chloride, from two coagulating baths, one based on potassium acetate and the other one based on potassium formate.

The test is carried out as follows. Two aqueous solutions of 420 ml. each are prepared, one of potassium formate and the other of potassium acetate, both having a concentration of 58% -(by weight). To each solution 80 niL, equivalent to 76 g., of pure dimethylformamide are added, two limpid and homogeneous solutions of 500 ml. being obtained. Each of these solutions is subsequently treated three successive times, each time with ml. of methylene chloride and shaken each time for one minute. Then the mixture is allowed to rest for about 15 minutes and it separates into two layers. The quantity of dimethylformamide extracted by the methylene chloride is then measured. The results are shown in the following table.

The table shows that three extractions have removed from the potassium acetate bath about 88% of the dimethylformamide and from the potassium formate bath about 98%, so that the first bath retains after treatment about-2% by volume of dimethylformamide, and the second bath only 0.3% by volume.

In addition to this economical advantage, when a potassium formate bath is used the two layers formed in the extraction separate more quickly end sharply and are clearer, which facilitates the recovery. The same advantages are found if other solvents are used for instance dimethyl acetamide, butyrolactone, ethylene carbonate; or if the polymer of acrylonitrile is not polyacrylonitrile but a different polymer, for instance a copolymer with itaconic acid or with vinylpyridines, or a copolymer or a graft polymer insoluble in water with cellulose acetate, with a polymer of the methyl mono-ester of itaconic acid, or with polyacrylic acid.

The invention is not limited to the particulars of the working examples described, but includes all those variants that can be carried out by persons in the art.

We claim:

1. A wet-spinning process for the manufacture of fila- 'ments of acrylonitrile polymers, comprising the steps of extruding a solution of a polymer of acrylonitrile in an organic solvent into a coagulating bath and thereafter stretching the resulting filaments in a stretching bath both baths comprising essentially aqueous solutions containing from 30 to 75% by weight of potassium formate.

2. A process according to claim 1, wherein the coagu lating bath contains from 0.5 to 30% by weight of the organic solvent of the extruded solution.

3. A process according to claim 1, wherein the stretching bath contains from 0.5 to 30% by weight of the organic solvent of the extruded solution.

4. A process according to claim 1, comprising maintaining the coagulating bath' at a temperature not below 20 C. andnotabove 50 C.

5. A process according to claim 1, comprising maintaining the stretching bath at a temperature not below C. and not above C.

No references cited. 

1. A WET-SPINNING PROCESS FOR THE MANUFACTURE OF FILAMENTS OF ACRYLONITRILE POLYMERS, COMPRISING THE STEPS OF EXTRUDING A SOLUTION OF A POLYMER OF ACRYLONITRILE IN AN ORGANIC SOLVENT INTO A COAGULATING BATH AND THEREAFTER STRETCHING THE RESULTING FILAMENTS IN A STRETCHING BATH BOTH BATHS COMPRISING ESSENTIALLY AQUEOUS SOLUTIONS CONTAINING FROM 30 TO 75% BY WEIGHT OF POTASSIUM FORMATE. 